1. Field of the Invention
The present invention concerns a method for generation of an imprint with a printing device operating according to a dot matrix principle (in particular an inkjet principle) in which a dot pattern is provided for the imprint, and with which printing device image points corresponding to the provided dot pattern are generated on a substrate. The invention furthermore concerns a corresponding arrangement for generation of such an imprint.
2. Description of the Prior Art
In the creation of imprints according to such a dot matrix principle as is normally used, for example, in present-day franking machines, a good compromise must be found between the imprint quality (thus, for example, the area coverage of the imprint) and (given the use of ink) the flow of the ink and the consumption of the printing medium (thus, for example, of the ink).
In order to keep the ink consumption optimally low EP 0 720 919 A1 proposes to not print certain image points that would otherwise be printed corresponding to the provided dot pattern, in order to achieve a thinning of the imprint. The thinning is achieved by generating a type of checkerboard pattern in an actual region to be printed over its entire surface according to the provided dot pattern, with every first image point in a row or in a column being printed while every second image point is omitted (thus is not printed). This has the disadvantage that a possibly visible and therewith undesired regular (interfering) pattern occurs in the imprint.
In order to avoid irregular edges in an imprint, according to EP 0 720 919 A1 an edge sharpening algorithm is provided that should ensure that edge points defining a contour of the imprint are always printed, and furthermore the printing of two image points immediately next to one another in a line is prevented. This has the disadvantage that a stripe pattern arises in the region of the contour.
Furthermore, given the use of print heads with a number of nozzle rows that exhibit a higher resolution than the provided dot pattern, it is known to print the image points with only every other nozzle row. In order to achieve a higher area coverage, intervening image points are printed in turn according to a predetermined scheme. This also has the disadvantage that undesired regular patterns are hereby again generated in the imprint.
These regular patterns can in fact be avoided by the use of a distinctly higher ink quantity, for example by reduction of the omitted (i.e. unprinted) image points. This, however, can result in too much ink being applied, which is not only undesirable from an economic standpoint but also results in the problem that the imprint can smear.
A further disadvantage of the known methods is that the area coverage or the degree of thinning of the imprint can be varied only in a relatively complicated manner, by the use of a different thinning scheme or modification of the scheme in use.